File:The Quarterly journal of the Geological Society of London (12734144164).jpg

FROM ALGIERS TO THE SAHARA.
115
and the French surveyors have ascer-
tained that some of the lagoons in the
neighbourhood are below the sea-level.
From inquiries I made at L'Aghouat,
I ascertained that the plateau on which
it is built spreads out as a promontory
in a south-easterly direction towards
the level of the main desert, descending
by slopes and terraces to the sea-level.
Mr. Tristram tells me that red sand-
stone, which he supposes to be of
Triassic age, rises up in the M'Zab
country to the S.E. of L'Aghouat. This
is probably a recurrence of the red
sandstone which comes to the surface
in the Sidi Makhelouf anticlinal.
Although there is good evidence of
a Posttertiary submergence of the dis-
trict surrounding L'Aghouat, the high
level of the sandhills may also be partly
attributed to the agency of wind, the
effect of which in transporting sand to
great distances must be seen to be fully
realized. My approach to L'Aghouat
was through a blinding sand-storm,
which was still in full force on the
following day, when on ascending one
of the rocky eminences over the town I
obtained my first view of the desert
plain. A bitter east wind was blowing,
and the light was quite subdued by the
sand-storm. Looking south over the
plain I could but dimly see the level
horizon through the murky haze

and
nearer the sudden gusts of wind were
picking up from the desert cloud-like
patches of sand, and whirling some of
them away towards the great smoky
mass of moving sand in the distance,
and heaping up the nearer clouds in
talus-like slopes against the boundary
escarpments. To the north, terrace
upon terrace of the cliffs of the Hauts
Plateaux, piled up in receding lines,
formed the boxmdary (Fig. 4). The
near view was equally remarkable.
East and west I looked along a broken
ridge of rocks, completely isolated in
the plain, crowned by handsome French
buildings and long lines of fortifica-
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